The documentary “Bully” is essential to see, whether you’re a parent or a kid, whether you’ve been on the giving or receiving end of such increasingly pervasive cruelty.

But it’s also frustrating to watch, because while the stories included here are undeniably moving by nature, they’re not exactly told in the most artful way, rendering “Bully” far less emotionally impactful than it might have been.

Director Lee Hirsch’s film grows repetitive and seems longer than its relatively brief running time. Tonally, it bounces with no rhyme or reason between a handful of students across the country who’ve suffered from bullying; technically, it feels a bit messy, with needless zooms and images that fade in and out of focus. Perhaps that was an intentional aesthetic choice. Either way, it’s distracting and headache-inducing.

Still, if “Bully” does nothing more than provide the impetus for a dialogue, it achieves its purpose.

Hirsch spent a year with about a half-dozen families with children who’ve been bullied at school – teased, abused, humiliated and ostracized – behavior which adults too often sweep aside with the cliche that kids will be kids.

Among them are David and Tina Long of Murray County, Ga., whose 17-year-old son, Tyler, hanged himself. Tina bravely shows the closet where the family found him, in his bedroom since turned into an office, and the death has turned the Longs’ quiet suburban life into a crusade for awareness.

Among the movie’s other stories is 12-year-old Alex, a scrawny kid from Sioux City, Iowa. His parents acknowledge he’s a bit weird but as his mom points out, he’d be the most devoted friend to anyone who would accept him. Hirsch’s camera captures Alex’s grueling daily school bus ride as big, mean kids use him as their punching bag. Alex has no idea how to stand up for himself and no adults seem capable of doing it for him (the assistant principal of his middle school comes off as especially clueless and inept).

In conservative Tuttle, Okla., 16-year-old Kelby has been shunned since she came out as a lesbian, as have her parents. She finds a small circle of friends who accept her as she is, including a girlfriend, and people who inspire her to get out of bed every morning, but she feels discouraged when she can’t open up more minds and hearts. Her parents’ evolution on the subject is inspiring to see.

These are just some of the stories Hirsch shares in “Bully.” Any one of them might have served as its own complete film. This is especially true of a tale that comes toward the end: that of Kirk and Laura Smalley, whose 11-year-old son, Ty, took his own life because of bullying. These are admittedly simple, small-town folks: avid hunters and St. Louis Cardinals fans with longtime family roots in the area who are forced to reexamine everything that defines them in a teary haze. Kirk’s honesty and purity of emotion are haunting, and our time with this family is tantalizingly brief.

As the mother of a 2-year-old boy, I’m glad “Bully” exists. As a film critic, I wish it were more accomplished.